I'm not sure if there's a fancier way to do this with the spriter object but you can just select the sprite you want after importing your animations and add an image point in Construct.. Afterward you treat spawning your bullet like you would with any other standard sprite object, by selecting that sprite and the imagepoint you want to use. I know you've already added an imagepoint in Spriter but I don't know how to use those features so I can't help from that side.